Hobbyist-friendly non-mechanical and/or non galvo-based scanners?

[krfkeith]

Hello,
This is my first post here, and I apologize if it's a stupid question, however, has anyone here, or elsewhere, ever built a scanner using some methodology besides galvo mirrors? I know you can buy acousto-optic modulators, but they seem way too expensive, and way too limited in maximum angle to be of use.

Does anyone have any suggestions for applications requiring greater speed and/or precision than galvos can do?

[Laserhobbit]

It would help if you explained the application you are considering for this alternative scanning method. it may be that some of the members here may have some feedback on the application rather than technology.

Also please tell us a little about yourself, some background and where your interests are. Most importantly please fill in your location, we are a really friendly bunch and it is possible there may be a member nearby willing to meet up and discuss.

Finally welcome to the best forum on the net

Cheers

Steve

[krfkeith]

Thanks for the reply!

Alright, let me try and explain my goal.

I'm sure many of you here are familiar enough with the various attempts to play old vector arcade games with laser projectors. While these have been very neat, they've also been very flickery from what I can tell. Though, to be fair, it's unclear to me to what extent the flicker is an artifact of the video recorder.

Anyhow, the major limitation of these is that a lot of vector games rely on the permanence of the of the phosphors as effects in their own right, something which I think laser projectors are necessarily going to have a hard time with. Secondly, as near as I can tell, galvos just simply aren't fast enough.

The idea I had, was instead to try and emulate the workings of a CRT more closely. That is, scan a phosphor screen with a UV laser. This is apparently already done, on a very limited commercial scale (for large video wall installations where the cost for an LCD or Plasma would be prohibitive). But apart from the fact that there is no consumer model, this is also a raster-scan technology.

So basically, the question comes down to. . .would it even be theoretically possible to scan the phosphor screen with galvo mirrors? Remember that since this isn't persistence-of-vision, you don't (in theory) have to worry about retrace. If not (as I suspect), what would be the most realistic (if any) way for a hobbyist to approach the problem of scanning the screen fast enough to "keep up" with the speed of the electron gun as expected by the game code. I don't quite understand how this unit compares to the pps metric given by galvo manufacturers with respect to scanning speed or slew rate or whatever, but I do know that apparently the Atari Asteroids game had a "1 Mhz" monitor, and can apparently operate acceptably on a monitor with a bandwidth of as low as 300 khz.

Anyway, thanks so much for reading, and I hope that helps clear up what I'm trying to accomplish! I hope I don't sound too insane now!

[laserist]

A video projector and a well designed emulator...

[krfkeith]

A video projector and a well designed emulator...

. . .can't come close to authentically emulating the look and feel of a true vector monitor unfortunately. As I mentioned, the games used the specific effects of the phosphors, and as such I can't really think of a way to properly emulate this without real phosphors.

[mixedgas]

Scanning the phosphors has been done. I've done it for work related reasons that had nothing to do with video.

You hit four issues:

1. UV diode lasers that you can easily access have very low power, about 800-1600 mW if you combine two of them with polarization.. They also have the wrong wavelength, about 380 nanometers. Anything better then that is extremely expensive or requires three phase power. If you have more then a hobbyist budget, I can suggest some better things.

2. The medium persistence phosphors are expensive and hard to obtain for governmental reasons.
I was told NO in very certain terms from domestic US Suppliers. Not to mention, without some very specialized position feedback and electronics, your limited to monochrome.

3. The conversion efficiency is not so great unless you pump at 266 nm, your better off with RGB lasers. 266 nanometer lasers, with a small, tight beam, are not inexpensive. If you sample all the users of this forum, maybe 5 have access to 266 nanometer UV lasers at home. Your alternative is a 380 nm diode that is only made by one manufacturer, or UV Argon ion laser, which is .001% efficient at best.

4. The vectors have to be re-processed for velocity compensation, Electron beams use stroke writing with sample and hold capacitors providing the control signals, and have no inertia for all practical purposes. Galvos need more care and feeding, because they have inertia. for a E-beam, the software issues the beginning and end co-ordinates. For a galvo, you add in extra vectors to speed up, slow, and stop the galvo. (If only it were that easy to describe) A good galvo has 2.5 KHz of bandwith, but that does not stop us from projecting simple vector games. Asteroids is a stock application that comes with certain laser show software.

See: http://www.jmargolin.com/vgens/vgens.htm If you use the Margolin described hardware with a galvo, you just see a few bright dots with distorted lines in-between.

As for laser scanning, there is AO, Galvo, and EO, and Raster using Polygons or Resonant Galvos. MEMS does not rate a mention here, if you want to do MEMs buy a stock video projector. EO is even more expensive then AO.

If your a good RF engineer, you can bring the AO costs down buy building your own drivers. You then need optics to expand the AO scan angle to something useful.

The solution is to split the game across several Galvo scan heads, which has been done.

There are legalities to be aware of if you use a laser projected game in large scale public access.

Search the forum for Lazy Mame and Laser Mame. Laser Mame is not exactly public access. I knew the guys who did Laser Mame, long ago.

About once I year I see the required AO gear on Ebay, but there is nothing in-expensive.


Steve

[krfkeith]

Wow, thank you so much for your excellent response, that was exactly the answers I was looking for.

1. Hmm, that does sound like a problem. What about TEA lasers? They're somewhat commonly made by hobbyists and can operate in UV range (IIRC). Efficiency is probably very low though.

2. Monochrome would be fine. I know some of the more esoteric ones (like red) are hard to find, but isn't the green used in old school tubes just ZnS:Cu? That's not really hard to find.

3. Ah, 266nm? That sounds like excimer territory.

4. I'm aware of the inertia problems. Someone on some site likened it to swinging around a light bulb on a string. . .you have much less direct control over the position. That being said, would an AOM based system have such problems? I know AOMs have to deal with rise time issues, but wouldn't the beam be relatively free of the sort of problems that are intrinsic to galvos?

Finally, you mentioned expanding optics for AO-based systems, I actually made a seperate thread (before I even read your response) about that very subject. If it wouldn't be too trouble, I posted a very rough schematic of my understanding of how such a thing would work. Do you think you could tell me whether I'm at least vaguely on the right track?


Once again, thank you so much for your response.

[mixedgas]

Phosphors used in Arcade tubes are P22 family, with controlled persistence. ZnS:CU has a very long persistence when excited by UV laser. ZnS:CU also comes in a variety of persistence ratings, depending on impurities.

TEA lasers have a max rep rate of a few 10s of Hz and a few nanosecond pulse length. They have lousy beam quality, and you'd just see a grid of moving dots.

266 nm is obtained by intracavity frequency doubling of 532 nm Nd:YAG lasers.

The AO expansion optics, I can discuss off forum. That took me years to figure out, and I can suggest books, but it is not something I will place in public domain.

Flicker, what flicker? Much of it comes from the video camera. Ok, so there is a little flicker..... This is ONE scan head, See Zoof's video below:

http://www.youtube.com/watch?v=cpD6atERJ08

[laserist]

. . .can't come close to authentically emulating the look and feel of a true vector monitor unfortunately. As I mentioned, the games used the specific effects of the phosphors, and as such I can't really think of a way to properly emulate this without real phosphors.

Hence the "well designed emulator" - of course you can emulate the phosphor's intensity decay...

[swamidog]

see the AAE project

http://pages.suddenlink.net/aae/

Hence the "well designed emulator" - of course you can emulate the phosphor's intensity decay...